6,020 research outputs found
A Martian Quarantine Risk Model
Structured model using loss functions to assess risk of using given decontamination procedure on all Martian unmanned landing craf
Refined Simulations of the Reaction Front for Diffusion-Limited Two-Species Annihilation in One Dimension
Extensive simulations are performed of the diffusion-limited reaction
AB in one dimension, with initially separated reagents. The reaction
rate profile, and the probability distributions of the separation and midpoint
of the nearest-neighbour pair of A and B particles, are all shown to exhibit
dynamic scaling, independently of the presence of fluctuations in the initial
state and of an exclusion principle in the model. The data is consistent with
all lengthscales behaving as as . Evidence of
multiscaling, found by other authors, is discussed in the light of these
findings.Comment: Resubmitted as TeX rather than Postscript file. RevTeX version 3.0,
10 pages with 16 Encapsulated Postscript figures (need epsf). University of
Geneva preprint UGVA/DPT 1994/10-85
The Reaction-Diffusion Front for in One Dimension
We study theoretically and numerically the steady state diffusion controlled
reaction , where currents of and particles
are applied at opposite boundaries. For a reaction rate , and equal
diffusion constants , we find that when the
reaction front is well described by mean field theory. However, for , the front acquires a Gaussian profile - a result of
noise induced wandering of the reaction front center. We make a theoretical
prediction for this profile which is in good agreement with simulation.
Finally, we investigate the intrinsic (non-wandering) front width and find
results consistent with scaling and field theoretic predictions.Comment: 11 pages, revtex, 4 separate PostScript figure
Observation of Vortex Pinning in Bose-Einstein Condensates
We report the observation of vortex pinning in rotating gaseous Bose-Einstein
condensates (BEC). The vortices are pinned to columnar pinning sites created by
a co-rotating optical lattice superimposed on the rotating BEC. We study the
effects of two different types of optical lattice, triangular and square. With
both geometries we see an orientation locking between the vortex and the
optical lattices. At sufficient intensity the square optical lattice induces a
structural cross-over in the vortex lattice.Comment: 4 pages, 6 figures. Replaced by final version to appear in Phys. Rev.
Let
Critical temperature of Bose-Einstein condensation in trapped atomic Bose-Fermi mixtures
We calculate the shift in the critical temperature of Bose-Einstein
condensation for a dilute Bose-Fermi mixture confined by a harmonic potential
to lowest order in both the Bose-Bose and Bose-Fermi coupling constants. The
relative importance of the effect on the critical temperature of the
boson-boson and boson-fermion interactions is investigated as a function of the
parameters of the mixture. The possible relevance of the shift of the
transition temperature in current experiments on trapped Bose-Fermi mixtures is
discussed.Comment: 15 pages, 2 figures, submitted to J. Phys.
Experimental studies of equilibrium vortex properties in a Bose-condensed gas
We characterize several equilibrium vortex effects in a rotating
Bose-Einstein condensate. Specifically we attempt precision measurements of
vortex lattice spacing and the vortex core size over a range of condensate
densities and rotation rates. These measurements are supplemented by numerical
simulations, and both experimental and numerical data are compared to theory
predictions of Sheehy and Radzihovsky [17] (cond-mat/0402637) and Baym and
Pethick [25] (cond-mat/0308325). Finally, we study the effect of the
centrifugal weakening of the trapping spring constants on the critical
temperature for quantum degeneracy and the effects of finite temperature on
vortex contrast.Comment: Fixed minor notational inconsistencies in figures. 12 pages, 8
figure
Production Efficiency of Ultracold Feshbach Molecules in Bosonic and Fermionic Systems
We investigate the production efficiency of ultracold molecules in bosonic
Rb and fermionic K when the magnetic field is swept across a
Feshbach resonance. For adiabatic sweeps of the magnetic field, the conversion
efficiency of each species is solely determined by the phase space density of
the atomic cloud, in contrast to a number of theoretical predictions. Our novel
model for the adiabatic pairing process, developed from general physical
principles, accurately predicts the conversion efficiency for {\it both}
ultracold gases of bosons and of fermions. In the non-adiabatic regime our
measurements of the Rb molecule conversion efficiency follow a Landau
Zener model, with a conversion efficiency that is characterized by the density
divided by the time derivative of the magnetic field.Comment: 5 pages, 3 figure
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